1. Field of the Invention
This invention relates to integrated circuit devices, and, in particular, to ways integrated circuit devices manipulate image data.
2. Description of Related Art
The advent of powerful VLSI chips made it possible for multiple tasks to be performed on a single chip. Multimedia signal processor (MSP) chips are examples of such powerful VLSI chips, and are often equipped with multitasking operating systems which are capable of running multiple digital signal processing (DSP) tasks virtually simultaneously, such as video and audio compression/decompression processing, modem operations, and facsimile operations. A typical multimedia computer system configuration 110 is shown in FIG. 1. The multitasking operating system provides convenience, improves productivity, and also achieves better utilization of an MSP. But running several computationally demanding DSP tasks, can overload the MSP. Video compression and decompression are two of such computationally demanding tasks that are frequently performed on an MSP.
Typical digital video images require vast amount of storage or channel bandwidth. Motion Picture Expert Group (MPEG) is an international committee charged with providing a standard for achieving compatibility between image compression and decompression equipment. Since its inception, two standards (referred hereinbelow as "MPEG-1" and "MPEG-2") have been proposed by MPEG. Each of these standards specifies both the coded digital representation of video signal for the storage media, and the process for decoding. Using MPEG-1 or MPEG-2 encoding on image data saves storage space for video data, that is, the encoding achieves data compression. Yet, MPEG-1 and MPEG-2 compression are computationally intensive due to several steps involved, one of which is a two-dimensional discrete cosine transform (2-D DCT), which performs multiple matrix multiplications. A video file encoded (i.e., compressed) and saved on a storage device has to be decoded (i.e., decompressed) before actual usage. (From now on, terms "encoding" and "compression" will be used interchangeably, and so will terms "decoding" and "decompression".) Decompression is also a computationally intensive process, as it involves reversing the steps of the 2-D DCT, called 2-D IDCT (inverse discrete cosine transform), or merely IDCT.
As a result of the heavy computational demand of a 2-D IDCT, when one or more decompression tasks (each of which perform IDCT) are involved, the number of tasks that can be reasonably run on a single processor becomes relatively small, diminishing the advantage of the multitasking operating system.
For example, each decompression task may take up 38% of the MSP's computational capacity. If, in an operating system, a third decompression task is submitted when two decompression tasks are already being carried out by the MSP, operating systems, the will reject running the third task, since running it will overload the MSP.
One of the previous approaches to deal with the overloading problem with respect to video data manipulation is to reduce the frame rate of the video output. This approach, however, produces a noticeably degraded video output which is perceptually very awkward.
What is needed is a cost-effective approach that will allow relatively more tasks to be run on a processor.